Supported chromium catalyst and its use for preparing homopolymers and copolymers of ethylene

ABSTRACT

A process for preparing supported, titanized chromium catalysts is disclosed. The process comprises A) bringing a support material into contact with a protic medium comprising a titanium compound and a chromium compound; B) optionally removing the solvent; C) optionally calcining the precatalyst obtained after step B); and D) optionally activating the precatalyst obtained after step B) or C) in an oxygen-containing atmosphere at from 400° C. to 1100° C.

This application is the U.S. national phase of International ApplicationPCT/EP2003/013914, filed Dec. 9, 2003, claiming priority to GermanPatent Application 10257740.4 filed Dec. 10, 2002, and the benefit under35 U.S.C. 119(e) of U.S. Provisional Application Nos. 60/446,936, filedFeb. 12, 2003 and 60/437,633 filed May 2, 2003; the disclosures ofInternational Application PCT/EP2003/013914, German Patent Application10257740.4 and U.S. Provisional Application Nos. 60/446,936 and60/437,633, each as filed, are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to novel supported, titanized chromiumcatalysts for the homopolymerization of ethylene and thecopolymerization of ethylene with α-olefins, a process for preparingthem and their use for the polymerization of olefins.

The present invention relates to novel supported, titanized chromiumcatalysts for the homopolymerization of ethylene and the copolymerizatonof ethylene with α-olefins, a process for preparing them and their usefor the polymerization of olefins.

BACKGROUND OF THE INVENTION

Ethylene homopolymers and copolymers of ethylene with higher α-olefinssuch as 1-butene, 1-pentene, 1-hexene or 1-octene can be prepared, forexample, by polymerization using supported titanium compounds, known asZiegler-Natta catalysts, or else using supported chromium compounds,known as Phillips catalysts. When the homopolymers and copolymers ofethylene are used, for example, for blown film extrusion, it isimportant that the polymers have a good balance between mechanicalproperties and processability.

Ethylene homopolymers and copolymers of ethylene with higher α-olefinssuch as 1-butene, 1-pentene, 1-hexene or 1-octene can be prepared, forexample, by polymerization using supported titanium compounds, known asZiegler-Natta catalysts, or else using supported chromium compounds,known as Phillips catalysts. When the homopolymers and copolymers ofethylene are used, for example, for blown film extrusion, it isimportant that the polymers have a good balance between mechanicalproperties and processability.

It is known that supported chromium catalysts are very suitable forproducing ethylene copolymers having good mechanical properties. Theproperties of the polymers obtained in the polymerization are dependenton the way in which the chromium catalyst used has been prepared, inparticular on the type of support material, e.g. its chemical structure,composition, surface area or pore volume, the type of chromium compoundused, the presence of further compounds, e.g. titanium compounds,aluminum alkyls or carbon monoxide, the order in which the variouscomponents are applied or the manner of calcination and activation. Itis a combination of the starting materials used together with theprocedure for application to a support which then gives the desiredchromium catalyst for the preparation of polymers having the propertyprofile required for the specific application.

The supported chromium catalysts are often titanized, i.e. they comprisenot only the chromium compound but also variable proportions of atitanium compound by means of which the molar mass distribution and theHLMI (high load melt index), for example, can be influenced. Theapplication of the titanium compound to the support is usually carriedout during the preparation of the hydrogel, giving an SiO₂—TiO₂ cogel.In this, the titanium dioxide is uniformly distributed throughout thesupport material. A disadvantage is that only a fraction of the totaltitanium oxide is available for polymerization at the pore surface ofthe catalyst. For this reason, numerous embodiments of titanizedchromium catalysts in which the titanium compound is applied in atargeted manner to the pore surface, usually in a step separate from thedoping of the chromium compound, have been developed.

Thus, for example, EP-A-882740 describes a process for preparing asupported chromium catalyst, in which the support material has aspecific surface area of from 450 to 600 m²/g and the chromium componentis applied to the support first and the titanium compound is appliedsubsequently, with the titanization being carried out at temperatures ofat least 300° C.

EP-A-882741 teaches that polyethylenes having favourable ultimatetensile strengths are obtained when using a supported chromium catalystwhose support material has a specific surface area of at least 400 m²/gand has been dehydrated before use and in the preparation of which thechromium component is applied to the support first and the titaniumcompound is applied subsequently.

The application of a mixture of a chromium compound and a titaniumcompound in an aprotic solvent to a support under aprotic conditions isdescribed in JP 54141893 and JP 57049605.

However, the preparation and handling of organometallic compounds underaprotic conditions is complicated and costly, since the solvents have tobe dried before use. In addition, only few chromium compounds aresoluble in aprotic media. An increase in the solubility of chromiumcompounds in aprotic solvents can often only be achieved by means of acomplicated synthesis.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel, lesscomplicated process for preparing supported, titanized chromiumcatalysts.

It is an object of the present invention to provide a novel, lesscomplicated process for preparing supported, titanized chromiumcatalysts.

We have found that this object is achieved by a process for preparingsupported, titanized chromium catalysts, which comprises the followingsteps:

-   A) bringing a support material into contact with a protic medium    comprising a titanium compound and a chromium compound,-   B) optionally removing the solvent,-   C) optionally calcining the precatalyst obtained after step B) and-   D) optionally activating the precatalyst obtained after step B)    or C) in an oxygen-containing atmosphere at from 400° C. to 1100° C.

The invention further provides novel supported, titanized chromiumcatalysts which are suitable for the polymerization of ethylene and, ifdesired, further comonomers and are obtainable by the process of thepresent invention. This novel supported, titanized chromium catalyst forthe homopolymerization of ethylene and the copolymerization of ethylenewith α-olefins will in the interests of brevity hereinafter be referredto as “chromium catalyst of the present invention”.

The invention also provides a process for preparing homopolymers ofethylene and copolymers of ethylene with α-olefins by polymerization ofethylene or mixtures of ethylene and α-olefins using at least onechromium catalyst according to the present invention, the homopolymersand copolymers of ethylene obtainable therefrom and their use forproducing films.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, it has now been found that homopolymers and especiallycopolymers of ethylene are obtained in particularly good yields whenusing the chromium catalysts of the present invention. The film productsobtained therefrom also have a very high puncture resistance.

Accordingly, it has now been found that homopolymers and especiallycopolymers of ethylene are obtained in particularly good yields whenusing the chromium catalysts of the present invention. The film productsobtained therefrom also have a very high puncture resistance.

In view of the prior art, it was not to be expected that this novelprocess would make it possible to obtain a very active catalyst whichleads to ethylene polymers which, when blown to produce films, displayparticularly good mechanical properties.

One constituent of the chromium catalyst of the present invention is thesupport material, in particular an inorganic solid, which is usuallyporous. Preference is given to oxidic support materials which may stillcontain hydroxy groups. The inorganic metal oxide can be spherical orgranular. Examples of such solids, which are known to those skilled inthe art, are aluminum oxide, silicon dioxide (silica gel), titaniumdioxide and their mixed oxides or cogels, and aluminum phosphate.Further suitable support materials can be obtained by modification ofthe pore surface, e.g. by means of compounds of the elements boron(BE-A-61,275), aluminum (U.S. Pat. No. 4,284,527), silicon (EP-A-0 166157) or phosphorus (DE-A 36 35 715). Preference is given to using asilica gel. Preference is given to spherical or granular silica gels,which in the case of the former may be spray dried.

Preferred support materials are finely divided silica xerogels which canbe prepared, for example, as described in DE-A 25 40 279. The finelydivided silica xerogels are preferably prepared by:

-   a) use of a particulate silica hydrogel which has a solids content    of from 10 to 25% by weight (calculated as SiO₂) and is largely    spherical, has a particle diameter of from 1 to 8 mm and is obtained    by    -   a1) introducing a sodium or potassium water glass solution into        a swirling stream of an aqueous mineral acid, both        longitudinally and tangentially to the main direction of flow,    -   a2) spraying the resulting silica hydrosol into a gaseous medium        so as to form droplets,    -   a3) allowing the sprayed hydrosol to solidify in the gaseous        medium,    -   a4) freeing the resulting largely spherical particles of the        hydrogel of salts without prior aging by washing,-   b) extraction of at least 60% of the water present in the hydrogel    by means of an organic liquid,-   c) drying of the resulting gel at up to 180° C. and a reduced    pressure of 13 mbar for 30 minutes until no further weight loss    occurs (xerogel formation) and-   d) adjustment of the particle diameter of the xerogel obtained to    from 20 to 2000 μm.

In the first step a) of the preparation of the support material, it isimportant to use a silica hydrogel which has a relatively high solidscontent of from 10 to 25% by weight (calculated as SiO₂), preferablyfrom 12 to 20% by weight, particularly preferably from 14 to 20% byweight, and is largely spherical. This silica hydrogel has been preparedin a specific manner as described in steps a1) to a4). The steps a1) toa3) are described in more detail in DE-A 21 03 243. Step a4), viz.washing of the hydrogel, can be carried out in any desired manner, forexample by the countercurrent principle using water which contains asmall amount of ammonia (pH up to about 10) and is at up to 80° C.

The extraction of the water from the hydrogel (step b)) is preferablycarried out using an organic liquid, which is particularly preferablymiscible with water, from the group consisting of C₁-C₄-alcohols and/orC₃-C₅-ketones. Particularly preferred alcohols are tert-butanol,i-propanol, ethanol and methanol. Among the ketones, preference is givento acetone. The organic liquid can also consist of mixtures of theabovementioned organic liquids; in any case, the organic liquid containsless than 5% by weight, preferably less than 3% by weight, of waterprior to the extraction. The extraction can be carried out in customaryextraction apparatuses, e.g. column extractors.

Drying (step c)) is preferably carried out at from 30 to 140° C.,particularly preferably from 80 to 110° C., and pressures of preferablyfrom 1.3 mbar to atmospheric pressure. For reasons of the vaporpressure, a rise in temperature should be accompanied by a rise inpressure and vice versa.

The adjustment of the particle diameter of the resulting xerogel (stepd)) can be carried out in any desired manner, e.g. by milling andsieving.

A further preferred support material is produced, for example, by spraydrying milled, appropriately sieved hydrogels which are for this purposemixed with water or an aliphatic alcohol. The primary particles areporous granular particles of the appropriately milled and sievedhydrogel which have a mean particle diameter of from 1 to 20 μm,preferably from 1 to 5 μm. Preference is given to using milled andsieved SiO₂ hydrogels.

In general, the mean particle diameter of the support particles is inthe range from 1 to 1000 μm, preferably in the range from 10 to 500 μmand particularly preferably in the range from 30 to 150 μm.

The mean average pore volume of the support material used is in therange from 0.1 to 10 ml/g, in particular from 0.8 to 4.0 ml/g andparticularly preferably from 1 to 25 ml/g.

In general, the support particles have a specific surface area of from10 to 1000 m²/g, in particular from 100 to 600 m²/g, in particular from200 to 550 m²/g.

The specific surface area and the mean pore volume are determined bynitrogen adsorption in accordance with the BET method, as described, forexample, by S. Brunauer, P. Emmett and E. Teller in Journal of theAmerican Chemical Society, 60, (1939), pages 209-319.

In addition, the support particles used according to the presentinvention have a mean pore diameter of from 80 to 250 Å, preferably from90 to 210 Å and particularly preferably from 95 to 200 Å. The mean porediameter in Å is calculated by dividing the numerical value of the meanpore volume (in cm³/g) by the numerical value of the specific surfacearea (in m²/g) and multiplying the result by 40 000. Suitable supportmaterials are also commercially available.

The support material can also have been partially or fully modifiedbefore use in the process of the present invention. The support materialcan, for example, be treated under oxidizing or non-oxidizing conditionsat from 200 to 1000° C., in the presence or absence of fluorinatingagents such as ammonium hexafluorosilicate. In this way, it is possible,for example, to vary the water and/or OH group content. The supportmaterial is preferably dried under reduced pressure at from 100 to 200°C. for from 1 to 10 hours before use in the process of the presentinvention.

In step A), the support-material is brought into contact with a proticmedium comprising, preferably consisting of, a titanium compound and achromium compound. The titanium compound and the chromium compound canbe dissolved or suspended in the protic solvent and are preferably bothdissolved. The titanium compound and the chromium compound can bebrought into contact with the solvent in any order, simultaneously or asa premixed mixture. The titanium compound and the chromium compound arepreferably mixed separately, in any order, with the solvent. Thereaction time is usually in the range from 10 seconds to 24 hours,preferably from 1 minute to 10 hours and particularly preferably from 10minutes to 5 hours, before the protic medium is brought into contactwith the support material.

As titanium compound, preference is given to using a tetravalentcompound of the formula (RO)_(n)X_(4−n)Ti, where the radicals R areidentical or different and are each an organosilicon or carboorganicsubstituent having from 1 to 20 carbon atoms, e.g. a linear, branched orcyclic C₁-C₂₀-alkyl group such as methyl, ethyl, n-propyl, isopropyl,n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, sec-pentyl,isopentyl, n-hexyl, cyclohexyl, n-heptyl or n-octyl, a C₆-C₁₈-aryl groupsuch as phenyl, 1-naphthyl, 2-naphthyl, 1-anthryl, 2-anthryl, 9-anthryland 1-penanthryl or a trialkylsilyl group such as trimethylsilyl ortriethylsilyl. R is preferably a linear or branched C₁-C₆-alkyl groupsuch as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl,isobutyl, tert-butyl, n-pentyl or n-hexyl. X can be a halogen such asfluorine, chlorine, bromine or iodine, preferably chlorine. n is from 0to 4 and is preferably 4. Mixtures of various titanium compounds canalso be used. The titanium compound is preferably soluble in the proticsolvent and preference is therefore given to using titaniumtetralkoxides because they have good solubilities in very many solvents.Apart from compounds of titanium with simple aliphatic alkoxides, it isalso possible for bifunctional ligands such as bisalkoxides orethoxyaminates to be present. Particularly useful compounds arebis(triethanolamine) bis(isopropyl)titanate or ammonium salts of lacticacid-titanium complexes which are soluble in water.

The chromium compounds can contain inorganic or organic groups.Preference is given to inorganic chromium compounds. Examples ofchromium compounds include chromium trioxide and chromium hydroxide andalso salts of trivalent chromium with organic and inorganic acids, e.g.chromium acetate, chromium oxalate, chromium sulfate and chromiumnitrate, and chelates of trivalent chromium, e.g. chromiumacetylacetonate. Among these, very particular preference is given tousing chromium(III) nitrate 9-hydrate and chromium acetylacetonate. Inpreferred chromium compounds the oxidation state of the chromium islower than 6 and preferentially chromium is in the oxidation state 2, 3or 4.

The protic medium is a solvent or solvent mixture comprising from 1 to100% by weight, preferably from 50 to 100% by weight and particularlypreferably 100% by weight, of a protic solvent or a mixture of proticsolvents and from 99 to 0% by weight, preferably from 50 to 0% by weightand particularly preferably 0% by weight, of an aprotic solvent or amixture of aprotic solvents, in each case based on the protic medium.

Protic solvents are, for example, alcohols R¹—OH, amines NR¹_(2−x)H_(x+1), C₁-C₅-carboxylic acids and inorganic aqueous acids suchas dilute hydrochloric acid or sulfuric acid, water, aqueous ammonia ormixtures thereof, preferably alcohols R¹—OH, where R¹ are each,independently of one another, C₁-C₂₀-alkyl, C₂-C₂₀-alkenyl, C₆-C₂₀-aryl,alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20carbon atoms in the aryl part or SiR² ₃, where R² are each,independently of one another, C₁-C₂₀-alkyl, C₂-C₂₀-alkenyl, C₆-C₂₀-aryl,alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20carbon atoms in the aryl part, and x is 1 or 2. Examples of possibleradicals R¹ or R² are: C₁-C₂₀-alkyl which may be linear or branched,e.g. methyl, ethyl, n-propyl, iso-propyl, n-butyl, isobutyl, tert-butyl,n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl or n-dodecyl, 5-to 7-membered cyloalkyl which may in turn bear a C₆-C₁₀-aryl group assubstituent, e.g. cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,cycloheptyl, cyclooctyl, cyclononyl or cyclododecyl, C₂-C₂₀-alkenylwhich may be linear, cyclic or branched and in which the double bond maybe internal or terminal, e.g. vinyl, 1-allyl, 2-allyl, 3-allyl, butenyl,pentenyl, hexenyl, cyclopentenyl, cyclohexenyl, cyclooctenyl orcyclooctadienyl, C₆-C₂₀-aryl which may bear further alkyl groups assubstituents, e.g. phenyl, naphthyl, biphenyl, anthranyl, o-, m-,p-methylphenyl, 2,3-, 2,4-, 2,5- or 2,6-dimethylphenyl, 2,3,4-, 2,3,5-,2,3,6-, 2,4,5-, 2,4,6- or 3,4,5-trimethylphenyl, or arylalkyl which maybear further alkyl groups as substituents, e.g. benzyl, o-, m-,p-methylbenzyl, 1- or 2-ethylphenyl, where two R¹ or two R² may in eachcase also be joined to form a 5- or 6-membered ring and the organicradicals R¹ and R² may also be substituted by halogens such as fluorine,chlorine or bromine. Preferred carboxylic acids are C₁-C₃-carboxylicacids such as formic acid or acetic acid. Preferred alcohols R¹—OH aremethanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,1-pentanol, 2-pentanol, 1-hexanol, 2-ethylhexanol, 2,2-dimethylethanolor 2,2-dimethylpropanol, in particular methanol, ethanol, 1-propanol,1-butanol, 1-pentanol, 1-hexanol or 2-ethylhexanol. The water content ofthe protic medium is preferably less than 20% by weight.

Examples of aprotic solvents are aliphatic and aromatic hydrocarbonssuch as pentane, hexane, heptane, octane, isooctane, nonane, dodecane,cyclohexane, benzene and C₇-C₁₀-alkylbenzenes such as toluene, xylene orethylbenzene.

The support material can be brought into contact with the protic mediumcomprising the titanium compound and the chromium compound in anydesired way. Thus, the mixture of protic medium, titanium compound andchromium compound can be added to the support material or the supportmaterial can be introduced into the mixture. The support material canalso be slurried in a suspension medium beforehand. The mixture ofsuspension medium used and protic medium comprises from 1 to 100% byweight, preferably from 50 to 100% by weight and particularly preferably100% by weight, of a protic solvent or a mixture of protic solvents andfrom 99 to 0% by weight, preferably from 50 to 0% by weight andparticularly preferably 0% by weight, of an aprotic solvent or a mixtureof aprotic solvents, in each case based on the mixture of the suspensionmedium used and the protic medium. This suspension medium is preferablylikewise the protic medium used according to the present invention.

The chromium compound is usually present in a concentration of from 0.05to 20% by weight, preferably from 0.1 to 15% by weight and particularlypreferably from 0.5 to 10% by weight, based on the protic medium. Thetitanium compound is usually present in a concentration of from 0.05 to30% by weight, preferably from 0.1 to 20% by weight and particularlypreferably from 0.5 to 15% by weight, based on the protic medium. Themolar ratio of chromium compound to titanium compound is usually in therange from 10:1 to 1:10, preferably from 5:1 to 1:7 and particularlypreferably from 4:1 to 1:5.

The support material is generally loaded in a weight ratio of supportedgel particles:Ti in the titanium compound of from 100:0.1 to 100:12, inparticular from 100:1 to 100:6, and a weight ratio of support gelparticles:chromium in the chromium compound of from 100:0.1 to 100:10,in particular from 100:0.3 to 100:3.

Reaction step A) can be carried out at from 0 to 150° C. For costreasons, preference is given to room temperature.

The solvent can optionally be removed in a subsequent step B),preferably at from 20 to 150° C. and pressures of from 10 mbar to 1mbar. Preference is given to removing part or all of the solvent. Theprecatalyst obtained in this way can be completely dry or can containsome residual moisture. The volatile constituents still present arepreferably present in an amount of not more than 20% by weight, inparticular not more than 10% by weight, based on the not yet activatedchromium-containing precatalyst.

The precatalyst obtained from reaction step B) can immediately besubjected to step D) or can be calcined beforehand at above 280° C. in awater-free inert gas atmosphere in step C). The calcination ispreferably carried out at from 280 to 800° C. in a fluidized bed forfrom 10 to 1000 minutes.

The intermediate obtained in this way from step B) or C) is thenactivated in step D) under oxidizing conditions, for example in anoxygen-containing atmosphere at from 400 to 1000° C. The intermediateobtained in step B) or C) is preferably activated directly in thefluidized bed by replacing the inert gas by an oxygen-containing gas andincreasing the temperature to the activation temperature. Theintermediate is advantageously heated at from 400 to 1100° C., inparticular from 500 to 800° C., in a water-free gas stream in whichoxygen is present in a concentration of above 10% by volume for from 10to 1000 minutes, in particular from 150 to 750 minutes, and then cooledto room temperature, resulting in the Phillips catalyst to be usedaccording to the present invention. The maximum temperature of theactivation is below, preferably at least 20-100° C. below, the sinteringtemperature of the intermediate from step B) or C). This oxidation canalso be carried out in the presence of suitable fluorinating agents suchas ammonium hexafluorosilicate.

A preferred process for preparing the supported, titanized chromiumcatalysts comprises the followings steps:

-   A) bringing a support material into contact with a protic medium    comprising a titanium compound and a chromium compound,-   B) removing the solvent,-   C) calcining the precatalyst obtained after step B) and-   D) activating the precatalyst obtained after step C) in an    oxygen-containing atmosphere at from 400° C. to 1100° C.

Particular preference is given to a process consisting of the steps A)to D).

The chromium catalyst of the present invention advantageously has achromium content of from 0.1 to 5% by weight, in particular from 0.3 to2% by weight, and a titanium content of from 0.5 to 10% by weight, inparticular from 1 to 5% by weight.

The catalyst systems of the present invention have a short inductionperiod in the polymerization of 1-alkenes.

The resulting chromium catalyst to be used according to the presentinvention can also be reduced, for example by means of ethylene and/orα-olefins, carbon monoxide or triethylborane, in suspension or in thegas phase before use or it can be modified by silylation. The molarratio of reducing agent to chromium (of the chromium catalyst accordingto the present invention to be reduced) is usually in the range from0.05:1 to 500:1, preferably from 0.1:1 to 50:1, in particular from 0.5:1to 5.0:1.

In suspension, the reduction temperature is generally in the range from10 to 200° C., preferably in the range from 10 to 100° C., and thepressure is in the range from 0.1 to 500 bar, preferably the range from1 to 200 bar.

The reduction temperature in fluidized-bed processes is usually in therange from 10 to 1000° C., preferably from 10 to 800° C., in particularfrom 10 to 600° C. In general, the gas-phase reduction is carried out inthe pressure range from 0.1 to 500 bar, preferably in the range from 1to 100 bar and in particular in the range from 5 to 20 bar.

In the gas-phase reduction, the chromium catalyst to be reduced isgenerally fluidized by means of an inert carrier gas stream, for examplenitrogen or argon, in a fluidized-bed reactor. The carrier gas stream isusually laden with the reducing agent, with liquid reducing agentspreferably having a vapor pressure of at least 1 mbar under normalconditions.

The chromium catalyst of the present invention is very useful for thepreparation of homopolymers of ethylene and copolymers of ethylene withα-olefins in the customary processes known for the polymerization ofolefins at temperatures in the range from 20 to 300° C. and pressures offrom 5 to 400 bar, for example solution processes, suspension processesin stirring autoclaves or in a loop reactor, stirred gas phases orgas-phase fluidized-bed processes, which may be carried out continuouslyor batchwise. The advantageous pressure and temperature ranges forcarrying out the process accordingly depend greatly on thepolymerization method.

In particular, temperatures of from 50 to 150° C., preferably from 70 to120° C., and pressures which are generally in the range from 1 to 400bar are set in these polymerization processes. As solvent or suspensionmedium, it is possible to use inert hydrocarbons such as isobutane orelse the monomers themselves, for example higher olefins such aspropene, butene or hexene in a liquefied or liquid state. The solidscontent of the suspension is generally in the range from 10 to 80% byweight. The polymerization can be carried out either batchwise, e.g. instirring autoclaves, or continuously, e.g. in tube reactors, preferablyin loop reactors. In particular, it can be carried out sing the PhillipsPF process as described in U.S. Pat. Nos. 3,242,150 and 3,248,179.

Among the polymerization processes mentioned, gas-phase polymerization,in particular in gas-phase fluidized-bed reactors, is preferredaccording to the present invention. It has been found that despite thevariety of processing steps and the spray-dried support materials, nofine dust is formed during the gas-phase polymerization. In general, itis carried out at a temperature which is at least a few degrees underthe softening temperature of the polymer. The gas-phase polymerizationcan also be carried out in the condensed, supercondensed orsupercritical mode.

The different polymerization processes, or even the same polymerizationprocess, can, if desired, be connected in series so as to form apolymerization cascade. However, the special catalyst composition makesit possible for the polymers according to the present invention to bereadily obtained from a single reactor.

Examples of suitable α-olefins which can be copolymerized with ethyleneare monoolefins and diolefins having from three to 15 carbon atoms inthe molecule. Well-suited α-olefins of this type are propene, 1-butene,1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene and 1-pentadeceneand also the conjugated and nonconjugated diolefins butadiene,penta-1,3-diene, 2,3-dimethylbutadiene, penta-1,4-diene, hexa-1,5-dieneand vinylcyclohexene. Mixtures of these comonomers can also be used.Preference is given to using 1-butene, 1-hexene or 1-octene, inparticular 1-hexene.

To control the molar mass, hydrogen can advantageously be used asregulator in the polymerization.

It has been found to be advantageous to carry out the polymerization ofthe 1-alkenes by means of the catalysts of the present invention in thepresence of organometallic compounds of elements of the first, second,third or fourth main group or of the second transition group of thePeriodic Table of the Elements. Well-suited compounds of this type arehomoleptic C₁-C₁₀-alkyls of lithium, boron, aluminum or zinc, e.g.n-butyllithium, triethylboron, trimethylaluminum, triethylaluminum,triisobutylaluminum, tributylaluminum, trihexylaluminum,trioctylaluminum and diethylzinc. Furthermore, C₁-C₁₀-dialkylaluminumalkoxides such as diethylaluminum methoxide are also well suited. It isalso possible to use dimethylaluminum chloride, methylaluminumdichloride, methylaluminum sesquichloride or diethylaluminum chloride.n-Butyllithium and trihexylaluminum are particularly preferred asorganometallic compound. Mixtures of the above-described organometalliccompounds are generally also well suited.

The molar ratio of organometallic compound:chromium is usually in therange from 0.1:1 to 50:1, preferably in the range from 1:1 to 50:1.However, since many of the activators, e.g. aluminum alkyls, can also beused at the same time for removing catalyst poisons (known asscavengers), the amount used is dependent on the impurities present inthe other starting materials. However, a person skilled in the art candetermine the optimum amount by means of simple tests.

The chromium catalysts of the present invention can also be usedtogether with another catalyst suitable for the polymerization ofα-olefins in the above polymerization processes. The chromium catalystof the present invention is preferably used together with anothersupported chromium catalyst customary for the polymerization ofα-olefins. The use of two different supported chromium catalysts isdescribed, for example, in WO 92/17511. The polymerization can also becarried out using two or more of the chromium catalysts of the presentinvention simultaneously. The polymerization is particularly preferablycarried out using a chromium catalyst according to the present inventiontogether with a supported, nontitanized chromium catalyst. Mixtures oftitanized and nontitanized supported chromium catalysts are described,for example, in U.S. Pat. No. 3,798,202, but in that case thetitanization is carried out only after the chromium component has beenapplied to a support.

The two different Phillips catalysts can be mixed before they come intocontact with the monomers and can then be introduced together into thereactor, or they can be introduced into the reactor separately from oneanother, for example at a plurality of points.

The homopolymers and copolymers of ethylene prepared according to thepresent invention usually have a density, measured in accordance withDIN 53479, in the range from 0.9 to 0.97 g/cm³, preferably in the rangefrom 0.92 to 0.96 g/cm³ and particularly preferably in the range from0.925 to 0.945 g/cm³, and a melt flow index (MI (190° C./2.16 kg) orHLMI (190° C./21.6 kg)), measured in accordance with DIN 53735 underdifferent loads (in brackets), in the range from 0 to 10 g/10 min,preferably in the range from 0.01 to 1 g/10 min and particularlypreferably in the range from 0.05 to 0.6 g/10 min, in the case of MI andin the range from 1 to 50 g/10 min, preferably in the range from 3 to 30g/10 min and particularly preferably in the range from 5 to 25 g/10 min,in the case of the HLMI.

The weight average molar mass M_(w) is generally in the range from 10000 to 7 000 000 g/mol, preferably in the range from 100 000 to 500 000g/mol. The molar mass distribution M_(w)/M_(n), measured by GPC (gelpermeation chromatography) at 135° C. in 1,2,4-trichlorobenzene usingpolyethylene standards, is usually in the range from 3 to 50, preferablyin the range from 8 to 30 and particularly preferably in the range from15 to 30.

In general, the ethylene polymers produced in the reactor are melted andhomogenized in an extruder. The melt flow index and the density of theextrudate can then differ from the corresponding parameters for thecrude polymer, but are also in the range specified according to thepresent invention.

In the olefin polymerization in which the catalyst prepared according tothe present invention is used, it is possible to prepare homopolymers ofethylene or copolymers of ethylene with a comonomer having from 3 to 12carbon atoms in an amount of up to 10 mol % of comonomer in thecopolymer. Preferred copolymers contain from 0.3 to 1.5 mol % of hexene,based on the polymer, particularly preferably from 0.5 to 1 mol % ofhexene.

The ethylene copolymer prepared according to the present invention canalso form mixtures with other olefin polymers, in particularhomopolymers and copolymers of ethylene. These mixtures can, on the onehand, be prepared by the above-described simultaneous polymerization ofa plurality of chromium catalysts. On the other hand, these mixtures canalso be obtained simply by subsequent blending of the polymers preparedaccording to the present invention with other homopolymers or copolymersof ethylene. MFI, HLMI, density, comonomer content, M_(w) andM_(w)/M_(n) of these mixtures are preferably likewise in the same rangesas those for the polymers which have been prepared using only atitanium-containing chromium catalyst according to the presentinvention.

In addition, the ethylene copolymers, polymer mixtures and blends canfurther comprise auxiliaries and/or additives known per se, e.g.processing stabilizers, stabilizers against the action of light andheat, customary additives such as lubricants, antioxidants, antiblockingagents and antistatics, and also, if desired, colorants. The type andamounts of these additives are well known to those skilled in the art.

The polymers prepared according to the present invention can also bemodified subsequently by grafting, crosslinking, hydrogenation or otherfunctionalization reactions which are known to those skilled in the art.

The polymers prepared according to the present invention are very usefulfor, for example, producing films on blown film plants at high outputs.Films comprising the polymers prepared according to the presentinvention have good mechanical properties. The high puncture resistanceof the films produced therefrom is also worthy of note.

The films obtained in this way are suitable, in particular, for thepackaging sector and for large, heavy duty sacks and also for the foodsector. Furthermore, the films have only a low blocking tendency and cantherefore be passed through machines without use of lubricants andantiblocking additives or with use of only small amounts thereof.

The Phillips catalyst prepared according to the present invention hasparticular unexpected advantages. It is very useful for thehomopolymerization and copolymerization of ethylene by the customary andknown particle form processes in a gas-phase fluidized-bedpolymerization. Here, it gives, at a high productivity, (co)polymershaving excellent morphology and good processability. In particular, thecatalyst of the present invention displays a good comonomerincorporation behavior and gives high productivities even at lowactivation temperatures. The (co)polymers prepared by means of thePhillips catalyst of the present invention are therefore particularlyuseful for processing by the blown film process and the blow moldingprocess.

The following examples illustrate the invention.

The productivity of the catalyst is reported as the amount of polymerisolated per amount of Phillips catalyst used in g.

The melt flow index was determined in accordance with ISO 1133 at 190°C. under a load of 21.6 kg (190° C./21.6 kg, HLMI) and under a load of2.16 kg (190° C./2.16 kg, MI.

The density [g/cm³] was determined in accordance with ISO 1183.

The bulk density (BD) [g/l] was determined in accordance with DIN 53468.

The environmental stress cracking resistance (ESCR) was determined inBasell's round disk indentor test (RI). Test conditions: round disks(produced from a pressed plate, diameter 38 mm, thickness: 1 mm, scoredon one side by means of a scratch having a length of 20 mm and a depthof 200 μm) are dipped at 50 or 80° C. into a 5% strength aqueoussolution of Lutensol® FSA and loaded by means of a gas pressure of 3bar. The time to occurrence of stress cracks which produce a pressuredrop in the measuring apparatus is measured (in h).

The measurement of the dart drop impact strength was carried out on 20μm films in accordance with ASTM 1709 A.

The Staudinger index (η)[dl/g] was determined at 130° C. on an automaticUbbelohde viscometer (Lauda PVS 1) using decalin as solvent (ISO 1628 at130° C., 0.001 g/ml of decalin).

The determination of the molar mass distributions and the means M_(n),M_(w) and M_(w)/M_(n) derived therefrom was carried out by means ofhigh-temperature gel permeation chromatography using a method based onDIN 55672 under the following conditions: solvent1,2,4-trichlorobenzene, flow: 1 ml/min, temperature: 140° C.,calibration using PE standards.

Abbreviations in the following tables:

T_(poly) Temperature during the polymerization M_(w) Weight average ofthe molar mass M_(n) Number average of the molar mass Density Polymerdensity DDI Dart drop impact ESCR Environmental stress crackingresistance % by volume Percentage by volume of the respective componentduring the polymerization Prod. Productivity of the catalyst in g ofpolymer obtained per g of catalyst used HLMI Melt flow index at aloading weight of 21.6 kg THA Amount of trihexylaluminum used ηStaudinger index mg cat. mg of the catalyst used in the polymerisationVinyl Vinyl groups in the polymer per (1000 C.)

EXAMPLES AND COMPARATIVE EXPERIMENTS Example 1

The support material was prepared as described in DE 2 540 279.

Preparation of the Silica Xerogel

A mixing nozzle as shown in the figure in DE-A 2 103 243 and having thefollowing data was utilized: the diameter of the cylindrical mixingchamber formed by a plastic tube is 14 mm, the length of the mixing zone(including after-mixing section) is 350 mm. The end of the mixingchamber nearest the inlet is closed off and near this end there is atangential inlet hole having a diameter of 4 mm for the mineral acid.Four further holes likewise having a diameter of 4 mm and the sameinflow direction for the water glass solution follow, with the spacingof the holes, measured in the longitudinal direction of the mixingchamber, being 30 mm. Accordingly, the ratio of length to diameter ofthe primary mixing zone is about 10:1. For the subsequent secondarymixing zone, this ratio is 15. As spraying nozzle, a flattened, slightlykidney shaped piece of tube was pushed over the outlet end of theplastic tube.

This mixing apparatus was supplied with 325 l/h of 33 percent strengthby weight sulfuric acid at 20° C. and an operating pressure of about 3bar and also 1100 l/h of water glass solution (prepared fromtechnical-grade water glass containing 27% by weight of SiO₂ and 8% byweight of Na₂O by dilution with water) having a density of 1.20 kg/l anda temperature of likewise 20° C. and a pressure of likewise about 3 bar.Progressive neutralization in the mixing chamber lined with the plastictube resulted in formation of an unstable hydrosol which had a pH of 7-8and remained in the after-mixing zone for about 0.1 s until completelyhomogenized before it was sprayed through the nozzle attachment into theatmosphere as a fan-shaped liquid jet. During its flight through theair, the jet broke up into individual droplets which, as a result of thesurface tension, took on a largely spherical shape and solidified toform hydrogel spheres within about one second while still in flight. Thespheres had a smooth surface, were clear as glass, contained about 17%by weight of SiO₂ and had the following particle size distribution:

>8 mm 10% by weight 6-8 mm 45% by weight 4-6 mm 34% by weight <4 mm 11%by weight

(The particle size distribution can be varied at will by use of othernozzle attachments.) The hydrogel spheres were collected at the end oftheir flight in a scrubbing tower which was filled almost completelywith hydrogel spheres and in which the spheres were washed free of saltsimmediately without aging by means of water containing a little ammoniaand having a temperature of about 50° C. in a continuous countercurrentprocess.

The spheres which had a diameter in the range from 2 to 6 mm wereisolated by sieving and 112 kg of these spheres were placed in anextraction vessel which had an inlet at the top, a sieve bottom andswan-neck shaped overflow which is connected to the bottom of the drumand keeps the liquid level in the drum sufficiently high for thehydrogel spheres to be completely covered with liquid. The hydrogel wasextracted by means of methanol.

The spheres obtained in this way were then dried (12 hours at 120° C.under a pressure of 20 mbar) until no further weight loss occurred at180° C. under a pressure of 13 mbar over a period of 30 minutes.

The spheres which had been dried in this way were subsequently milledand the xerogel particles which have a diameter of from 40 to 300 μmwere isolated by sieving. The pore volume was 1.9 ml/g.

39 ml of titanium tetraisopropoxide were added to a solution of 11.6 gof chromium(III) nitrate nonahydrate (Cr(NO₃)₃x9H₂O) in 700 ml ofmethanol. The solution of chromium(III) nitrate nonahydrate and titaniumtetraisopropoxide in methanol was clear and displayed no turbidity. Thesolution obtained in this way was added to 150 g of the above-describedsilica gel support. The suspension was stirred for 1 hour and thenevaporated to dryness on a rotary evaporator at 80° C. with applicationof a vacuum. The precatalyst-obtained in this way contains 1% by weightof chromium and 4% by weight of titanium, based on the weight of theprecatalyst.

Comparative Example C1

Example 1 was repeated without addition of titanium tetraisopropoxide.The precatalyst obtained in this way contains 1% by weight of chromium,based on the weight of the precatalyst.

Example 2

400 g of chromium(III) nitrate nonahydrate were dissolved in 6.5 l ofmethanol while stirring in a dissolution reactor. After stirring for onehour, 0.97 l of titanium tetraisopropoxide were added and the mixturewas stirred for another 5 minutes. This solution was subsequently pumpedover a period of 1 hour onto 5 kg of the silica gel support SylopolSG332 5N (commercially available from Grace) in a double cone drier. Thedissolution reactor was then rinsed with 1.5 l of methanol which wasthen likewise added to the support. The suspension was then stirred for1 hour and subsequently heated to 95° C. and the methanol was distilledoff at 900 mbar. After about 3 hours, the pressure was reduced to 300mbar and the product was dried under these conditions for a further 2hours. The precatalyst obtained in this way contains 1% by weight ofchromium and 3% by weight of titanium, based on the weight of theprecatalyst.

Comparative Example C2

The procedure of Example 2 was repeated using 5 kg of the silica gelsupport Sylopol SG332 5N and 120 g of chromium(III) nitrate nonahydratebut without addition of titanium tetrapropoxide. The precatalystobtained in this way contains 0.3% by weight of chromium, based on theweight of the precatalyst.

Example 3

1000 g of chromium(III) nitrate nonahydrate and 21 l of methanol weremixed with stirring in a dissolution reactor. After stirring for onehour, 2.3 l of titanium tetraisopropoxide were added to this solutionand the mixture was stirred for 5 minutes. This solution wassubsequently pumped over a period of 1 hour onto 18 kg of the silica gelsupport XPO2107 (commercially available from Grace) (which had beendried beforehand at 130° C. and 10 mbar for 7 hours in this double conedrier) in a double cone drier which was rotated uniformly. After theaddition, the dissolution reactor was rinsed with 5 l of methanol andthis rinsing solution was likewise added to the silica gel support. Thesuspension was stirred for a further 1 hour and was then dried at 90° C.with application of a vacuum until a pressure of 10 mbar at atemperature of 100° C. was reached after a period of 1 hour. Theprecatalyst obtained in this way contains 0.7% by weight of chromium and2% by weight of titanium, based on the weight of the precatalyst.

Comparative Example C3

3.5 l of titanium tetraisopropoxide were mixed with 20 l of heptanewhile stirring in a dissolution reactor. After stirring for 10 minutes,the solution was pumped over a period of one hour onto 18 kg of thesilica gel support XPO2107 (which had been dried beforehand at 130° C.and 10 mbar for 7 hours in this double cone drier) in a double conedrier which was rotated uniformly. The dissolution reactor was rinsedwith 5 l of heptane and this rinsing solution was likewise transferredinto the double cone drier. The suspension was then stirred for 1 hour.It was subsequently dried at 90° C. with application of a vacuum until apressure of 10 mbar at a temperature of 100° C. was reached after 1hour. 1000 g of chromium(III) nitrate nonahydrate and 23 l of methanolwere subsequently mixed while stirring in the dissolution reactor. Afterstirring for 1 hour, this solution was pumped over a period of 1 houronto the supported titanium compound in the rotating double cone drier.After the addition, the dissolution reactor was rinsed with 5 l ofmethanol and the rinsing solution was likewise transferred to the doublecone drier. The suspension was stirred for a further 1 hour and thendried at 90° C. with application of a vacuum until a pressure of 10 mbarat a temperature of 100° C. was reached after 1 hour. The precatalystobtained in this way contains 0.7% by weight of chromium and 3% byweight of titanium, based on the weight of the precatalyst.

Activation

Activation was carried out at 600 or 650° C. by means of air in afluidized-bed activator. To activate the precatalyst, it was heated to300° C. over a period of 1 hour, kept at this temperature for 1 hour,subsequently heated to the desired activation temperature, kept at thistemperature for 2 (Examples 1 and C1) or 5 hours (Examples 2, 3, C2 andC3) and subsequently cooled. Cooling below 300° C. was carried out undernitrogen. The precatalysts from Examples 1, C1 and C2 were heated to anactivation temperature of 750° C., the precatalyst from Example 2 washeated to an activation temperature of 600° C. and the precatalysts fromExamples 3 and C3 were heated to an activation temperature of 520° C.

Polymerization

The polymerization experiments in Table 1 were carried out under theconditions specified in Table 1 at a total pressure of 40 bar and anoutput of 25 kg/h in a 180 l PF loop reactor (=particle-forming loopreactor) (suspension medium: isobutane). The catalysts described inExamples 1 and C1 served as catalyst.

The polymerization experiments in Table 2 were carried out in acontinuous gas-phase fluidized-bed reactor (Lupotech G as described inWO99/29736 A1) under the conditions specified in the tables at a totalpressure of 20 bar and an output of 50 kg/h.

The products prepared in the gas-phase process were granulated at 200°C. under protective gas on a ZSK 40. Processing to produce films wascarried out on a blown film plant from W&H provided with a 60/25Dextruder. The catalysts described in Examples 2, C2, 3 and C3 served ascatalyst.

The results of the polymerizations and product tests are summarized inthe tables.

TABLE 1 Polymerization in the loop reactor Catalyst T_(Poly) % by volume% by volume Prod. Bulk density HLMI Density ESCR from Ex. [° C.] of C₂H₄of C₆H₁₂ [g/g] [g/l] [g/10 min] [g/cm³] Mw/Mn 50° C. [h] 1 104.5 15 0.1115625 466 12.7 0.9557 14 4 V1 106.6 10.1 0.14 5100 470 9.9 0.9565 12 6

TABLE 2 Polymerization in the gas phase Catalyst T_(Poly) THA % byvolume % by volume Prod. HLMI Density ESCR DDI from Ex. [° C.] [g/h] ofC₂H₄ of C₆H₁₂ [g/g] [g/10 min] [g/cm³] Mw/Mn 80° C. [h] [g] 2 113 0.4554.8 0.39 3799 25.8 0.9393 20 17 V2 112.2 0.4 55.4 0.33 7136 23.6 0.939410.2 13 3 103.5 0.5 53.4 1.05 3692 19.6 0.9323 25.5 163 V3 103.5 0.552.8 1.02 2921 16.5 0.9339 35.2 158

Example 4

1430 g of chromium(III) nitrate nonahydrate and 26 l of methanol weremixed with stirring in a dissolution reactor. After stirring for onehour, 2.3 l of titanium tetraisopropoxide were added to this solutionand the mixture was stirred for 5 minutes. This solution wassubsequently pumped over a period of 1 hour onto 18 kg of the silica gelsupport XPO2107 (commercially available from Grace). After the addition,the dissolution reactor was rinsed with 4 l of methanol and this rinsingsolution was likewise added to the silica gel support. The suspensionwas stirred for a further 1 hour and was then dried at 95° C. withapplication of a. The precatalyst obtained in this way contains 1% byweight of chromium and 2% by weight of titanium, based on the weight ofthe precatalyst.

Comparative Example C4

Di-tert.butylchromate was prepared by adding to a suspension of 4.86 gCrO₃ and 10 g MgSO₄ in 300 ml of hexane a solution of 9.45 ml oftert.-butanol in 50 ml hexane. After stirring for 15 min the solutionwas filtered to give a hexane solution of di-tert.butylchromate.

31.5 ml of titanium tetraisopropoxide and the di-tert.butylchromatesolution were added together onto 250 g of the silica gel supportXPO2107 (commercially available from Grace). The suspension was thenstirred for 1 hour. The hexane was distilled off and the resulting solidwas subsequently dried at 80° C. with application of a vacuum. Theprecatalyst obtained in this way contains 1% by weight of chromium and2% by weight of titanium, based on the weight of the precatalyst.

Activation

Activation was carried out at 520° C. by means of air in a fluidized-bedactivator as described above.

Polymerization

The polymerization experiments in Table 3 were carried out at a totalpressure of 40 bar, 100° C. for 90 min in a 1 l autoclave reactor(suspension medium: isobutane 400 ml, 10 ml hexene). The catalystsdescribed in Examples 4 and C4 served as catalyst. Both showed aproductivity of about 6000 g of polymer per g catalyst. The new catalystgave ethylene copolymers with a higher molecular weight (Mw and Mn) anda broader molecular weight distribution (Mw/Mn) with about the samedensity than the catalyst prepared in an aprotic medium (comparativeexample C4).

TABLE 3 Polymerization in the autoclave reactor Catalyst mg THA: η MwDensity Mw/ from Ex. Kat. Cr (mol) [dl/g] [g/mol] [g/cm³] Mn Vinyl 4 451:12 6.68 515388 0.9434 61.54 1.61 V4 44 1:13 4.39 381997 0.9446 55.812.04

1. A process for preparing supported, titanized chromium catalysts,which comprises the following steps: A) in a single step, bringing asupport material into contact with a protic medium having a watercontent less than 20% by weight and comprising a titanium compound and achromium compound, wherein the protic medium comprises an alcoholselected from the group consisting of methanol, ethanol, 1-propanol,1-butanol, 1-pentanol, 1-hexanol, and 2-ethylhexanol; B) optionally,removing the protic medium, thereby forming a precatalyst; C)optionally, calcining the precatalyst obtained after step B); and D)optionally, activating the precatalyst obtained after step B) or C) inan oxygen-containing atmosphere at from 400° C. to 1100° C.
 2. Theprocess as claimed in claim 1, wherein the support material is a silicagel.
 3. The process as claimed in claim 1, wherein the support materialis a silica xerogel.
 4. The process as claimed in claim 1, wherein thechromium compound is an inorganic chromium compound.
 5. The process asclaimed in claim 4, wherein the inorganic chromium compound ischromium(III) nitrate nonahydrate.
 6. The process as claimed in claim 1,wherein the titanium compound is titanium tetraisopropoxide, titaniumtetra-n-butoxide or a mixture thereof.
 7. The process as claimed inclaim 1, wherein the protic medium is methanol.